The present invention relates to an injector for injecting fuel into a cylinder of an in-cylinder injection type internal combustion engine.
FIG. 3 shows a structure for installing a conventional in-cylinder injector, which is described in Japanese Laid-Open Patent Publication No. 2000-9000. An in-cylinder injector 100 is installed in a socket 111, which is formed in a cylinder head 110 of an internal combustion engine. The socket 111 has a stepped portion, shaped in correspondence with the distal portion of the injector 100. To install the injector 100, a nozzle 101 of the injector 100 is inserted into a linear portion 112 of the socket 111, and a large diameter portion 102 of the injector 100 is loosely fitted in an outer opening 113 of the socket 111.
The upper end of the injector 100 is inserted in a delivery pipe 120. The injector 100 is fastened to the delivery pipe 120 by a screw 121. An arm 122 extending from the delivery pipe 120 is fastened to the cylinder head 110 via an insulator 123. In this way, the delivery pipe 120 and the injector 100 are fixed to the cylinder head 110.
An annular groove 103 extends along the outer surface of the nozzle 101 at the axial middle portion of the injector 100. An annular seal 104 is tightly fit in the annular groove 103. The annular seal 104 is elastically deformed when the nozzle 101 is inserted into the linear portion 112 of the socket 111. The annular seal 104 enables the injector 100 to be held in the socket 111 in a non-contact manner (i.e., in a floating state) while preventing leakage of combustion gas from the internal combustion engine. The annular seal 104 is usually made from a fluorocarbon resin, such as polytetrafluoroethylene (PTFE), or an elastic resin with high heat resistance, such as fluorocarbon rubber.
Due to the structure of the in-cylinder injector, the annular seal 104, which is a gas seal, is directly affected by the high temperature and high pressure of the combustion gas. This may deteriorate or melt the gas seal, even though the gas seal is made from a resin with high heat resistance. To prevent such deterioration and melting of the gas seal, the gas seal is separated from the distal end of the injector nozzle by a certain distance.
However, the distance between the gas seal and the nozzle end may result in a tendency for high-temperature combustion gas flowing to the distal portion of the nozzle 101. This would increase the temperature at the distal portion and form deposits on the distal portion. To solve this problem, another gas seal may be arranged on the distal portion of the nozzle to prevent high-temperature combustion gas from flowing to the distal portion. However, a plurality of gas seals attached to the nozzle would increase the load required to insert the injector in the socket and lower efficiency when installing the injector or performing maintenance work on the injector.